GS750 Re-jetting question

noahdog

noahdog

Been Around the Block
My brother has a 79 Suzuki GS750 that had pods when he got it. I'm pretty positive it was never re-jetted properly for the pods. Does anyone happen to know what jets he might need?
 
That's a great rule of thumb assuming that it has stock jets in it and that it's running lean.

Take it to a dyno and have them run the gas analysis and re-jet it on the dyno. that way you get what it needs - not what we think it probably ought to need.
 
Good suggestion, teezer, but not a lot of people are willing to fork out $100+ in dyno fees to simply rejet a bike for simple modifications to the inlet and/or exhaust. I certainly wouldn't pay it, although a simple dyno run in and of itself may get my hard-earned at some stage.

I had a GS850 with pods and 4-1 exhaust, and the 2 mainjet sizes over standard seems about right. If it is running #110 mains now, then I would try 120's in there and see how you go.

Cheers - boingk
 
best buy two sets of jets two sizes up so you can test incremently. Also know that things like temperature and humidity effect jetting as well, so there's not a 'cure-all' jetting for intake/exhaust custom set-ups.
 
I run 115 mains, 15 pilots (down from 17.5 stock) and the needle clip one position rich on my '77 gs750. It's still not perfect but it's probably the best I've had it after much experimentation. One of the hardest spots to nail perfectly is the cross-over from the pilot to the main jet. I think the gs750 was designed to idle with quite a high amount of throttle active. This means that when you install bigger mains, it'll start idling rich on you which will probably manifest as stutters and drop offs when it's idling.

Here's the kicker though: gs750s HATE pods. I had to install mine because when I got the bike the air box had been gutted out by some rodent that had lived in it for the 30 odd years the bike sat in a horse barn. I've considered tracking down a replacement box for awhile now, even considered going to filtered velocity stacks. From the other people I've talked to (including people that raced gs750s and 1000s in the 80s), the flat spot at 3,500 rpm never goes away as long as you're running pods.

Also, this should probably be in the cafe help section.
 
Also, check your needle clips. The VM28 carbs had really cheesy needles that wore pretty quickly. With 40k miles on my bike the first time I pulled them the clip seats were so worn I was afraid the needles might just drop loose. They were definitely worn enough that they could have been swinging around in the main jet and causing flow issues.
 
Hi There
I am a new Owner of a GS750 1977
It has been honed up to a 850,with 750 Cam shafts.

When i got it it had Aluminium funnels on the air intake (no filter)
It was dead belo 3600rpm and died out arund 7000rpm giving 140kph.
It used oceans of gas and ran approx 100km on a Tank (18L)

so i searched and found an original airbox and refurbished it. with (filter K&N), rubber and everything.
I also took apart the carbs and gave them a total cleaning, gaskets, float neetle + seat, changed main jets from 122.5 to 110.

Now the machine is dead before 4000 and after 5500 giving 120kph

when outside 4000/5500 it kinda sounds sick also when letting go of the gas while driving

Any Ideas ??
 
Today I took off the airbox and installed pod filters...
still with 110main jets
still almost dead below 3500rpm (think its drowning there) but it runs almost perfect between 4500 and 7500

idle is also super
but in the low rpm its not taking any throttle and chokes up.

is that the pilot jet i need resizing ??

if i put the airbox back on,,, should I then go even lower on jets maybe 100 or 105 ??

any inputs ideas advices ??
 
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